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The gas, which is colourless, is heavier than air, consequently heavy concentrations
are often found at floor level in the early stages of a treatment. However, the gas is
not difficult to disperse after an operation.
Apart from this density effect, the gas has greater powers of penetration than most
other fumigants in common use and this applies not only to penetration into commodities
but also through walls and sealing materials. A high standard of maintenance and sealing
is necessary in rooms to be used for fumigations using methyl bromide.
The penetration powers of methyl bromide, the absence of smell, thelack of immediate
symptoms of poisoning and the long term effect of poisoning, make it essential that
adequate precautionary measures should be taken at all stages from the manufacture of
the fumigant to the declaration of freedom from danger at the conclusion of operations.
The precautionary measures and the additional precautions for the treatments of ships
which are to be followed are laid down in a Home Office Pamphlet dated 1960.
The fumigation of ships by methyl bromide, usually for disinsection purposes, occurs
only occasionally in the Port of London.
The exposure to the gas depends on the concentration and on the period and purpose
of the exposure. For example in the case of a ship with completely empty holds, 12 ozs
of liquid per 1,000 cu. ft. for 12 hours would eradicate a rodent infestation in the holds,
whereas a minimum concentration of 32 ozs per 1,000 cu. ft. for 24 hours would be
required in the case of Khapra beetle infestation.
The following are the names of the firms approved for carrying out the deratting of ships: —
Contra-Pest Service Ltd.
Rentokil Laboratories Ltd.
(iv) Progress in Rat Proofing of Ships
No change.

677 Mice were also destroyed, 27 in vessels and 650 in shore premises.